I think your graphs reflect your customer's access more than preferences. For instance, do your users really prefer reading your content on Android tablets, or do more of your users own Android tablets (approximately $199) than do iPads (approx. $500 +). Also, smart phones are becoming ubiquitous, therfore more likely to be used by default.

Most publishers create ebooks in all formats figuring it doesn't matter whether mobi is more important than EPUB or if the content is read on an iPad more frequently than on a mobile phone. That approach means these publishers have no idea how their content is being consumed. It also means they ...